An efficient approach for treating composition-dependent diffusion within organic particles

Journal Article · 07 September 2017 · Atmospheric Chemistry and Physics (Online)

DOI: https://doi.org/10.5194/acp-17-10477-2017 · OSTI ID:1393748

O'Meara, Simon ^[1]; Topping, David O.  ^[1]; Zaveri, Rahul A.  ^[2]; McFiggans, Gordon ^[1]

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1. Univ. of Manchester, Manchester (United Kingdom)
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Mounting evidence demonstrates that under certain conditions the rate of component partitioning between the gas and particle phase in atmospheric organic aerosol is limited by particle-phase diffusion. To date, however, particle-phase diffusion has not been incorporated into regional atmospheric models. An analytical rather than numerical solution to diffusion through organic particulate matter is desirable because of its comparatively small computational expense in regional models. Current analytical models assume diffusion to be independent of composition and therefore use a constant diffusion coefficient. To realistically model diffusion, however, it should be composition-dependent (e.g. due to the partitioning of components that plasticise, vitrify or solidify). This study assesses the modelling capability of an analytical solution to diffusion corrected to account for composition dependence against a numerical solution. Results show reasonable agreement when the gas-phase saturation ratio of a partitioning component is constant and particle-phase diffusion limits partitioning rate (<10% discrepancy in estimated radius change). However, when the saturation ratio of the partitioning component varies, a generally applicable correction cannot be found, indicating that existing methodologies are incapable of deriving a general solution. Until such time as a general solution is found, caution should be given to sensitivity studies that assume constant diffusivity. Furthermore, the correction was implemented in the polydisperse, multi-process Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) and is used to illustrate how the evolution of number size distribution may be accelerated by condensation of a plasticising component onto viscous organic particles.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 1393748
• Report Number(s): PNNL-SA--122836; KP1701000
• Journal Information: Atmospheric Chemistry and Physics (Online), Journal Name: Atmospheric Chemistry and Physics (Online) Journal Issue: 17 Vol. 17; ISSN 1680-7324
• Publisher: European Geosciences UnionCopyright Statement
• Country of Publication: United States
• Language: English